The present invention relates to novel method and apparatus for making flexible bags, such as flexible bags containing potato chips, corn chips or the like.
The current state-of-the-art in the manufacture of flexible bags from flexible packaging material involves the (a) forming of a sheet of flexible packaging material into a tubular shape, (b) continuously sealing the longitudinal seam to form the sealed tubular member, (c) providing a bottom seal across the entire width of the tubular member, (d) filling the tube with product and (e) providing a top seal across the entire width of the tube to totally enclose the product within the bag. The vast majority of such bags are provided with seals which are induced by the application of heat, either by melting an adhesive specially provided at the seal location or by physically melting the layers of the packaging material to be sealed to one another without the use of adhesives. In either event, sufficient heat must be applied to either melt the adhesive or melt the packaging material, a process that has over the years proved generally satisfactory, but which has been rate-limiting in the production of many packaged food products and which has resulted in manageable but undesirable high rates of failure of the seals produced thereby.
With the advent of new technologies resulting in ever-faster rates of processing of various food products (e.g., potato chips, corn chips, pretzels, cookies, etc.) these technologies have not yet been fully recognized due to the relatively slow sealing rates of currently available packaging machines. One way to take advantage of the higher rates of production is to increase the number of packaging machines, which has to date been generally unacceptable due to the extremely high capital costs required and the space-availability problems related thereto. It has been suggested that the rate of packaging can be increased by simply increasing the heat applied to the seal area, thereby reducing the residence time necessary to effect the heat seal. However, most conventional packaging materials are not capable of withstanding such high temperatures without inducing severe damage to dimensional stability properties of the packaging material as a result.
Seals produced by conventional heat sealing methods are seldom uniform in strength, either from bag to bag or even across the seal on a particular individual bag. It is extremely difficult to maintain uniform temperatures or pressures across the sealing dies or jaws of conventional packaging machines. Uniformity is impeded by the presence of the back seal in the "middle" of the end seal which physically resists equalized pressure or transmission of heat across the seal width. Because most packaging materials contain multiple plies, one of which is generally intended as the sealing ply, the additional plies physically resist or impede uniform transmission of heat throughout the packaging material to be sealed. As a result, most packaging materials contain a relatively expensive sealant layer which would desirably be removed by users of such materials.